/*
 * hyperloglog.h
 *
 * 一个简单的 HyperLogLog 基数估算器实现
 *
 * Portions Copyright (c) 2014-2022, PostgreSQL Global Development Group
 *
 * 基于 Hideaki Ohno 的 C++ 实现。Ohno 原始版本的版权条款（MIT 许可）如下。
 *
 * src/include/lib/hyperloglog.h
 */

/*
 * Copyright (c) 2013 Hideaki Ohno <hide.o.j55{at}gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the 'Software'), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#ifndef HYPERLOGLOG_H
#define HYPERLOGLOG_H

/*
 * HyperLogLog 是一种计算集合中不同条目数量的近似技术。
 * 重要的是，它通过使用固定量的内存来实现。有关更多信息，
 * 请参见 2007 年的论文 "HyperLogLog: the analysis of a near-optimal
 * cardinality estimation algorithm"。
 *
 * hyperLogLogState
 *
 *		registerWidth		寄存器宽度，以比特为单位（"k"）
 *		nRegisters			寄存器数量
 *		alphaMM				alpha * m ^ 2（见 initHyperLogLog()）
 *		hashesArr			哈希数组
 *		arrSize				hashesArr 的大小
 */
typedef struct hyperLogLogState
{
	uint8		registerWidth;
	Size		nRegisters;
	double		alphaMM;
	uint8	   *hashesArr;
	Size		arrSize;
} hyperLogLogState;

extern void initHyperLogLog(hyperLogLogState *cState, uint8 bwidth);
extern void initHyperLogLogError(hyperLogLogState *cState, double error);
extern void addHyperLogLog(hyperLogLogState *cState, uint32 hash);
extern double estimateHyperLogLog(hyperLogLogState *cState);
extern void freeHyperLogLog(hyperLogLogState *cState);

#endif							/* HYPERLOGLOG_H */
